Production of cyclohexane from petroleum



Patented Apr. 11,1945

' PRODUCTION OF CYCLOHEXANE FR/OM PETROLEUM Donald L. Fuller and Bernard S. Greensl'elder,

Oakland, vCalif assignors to Shell Development Company, San Francisco, Calif., a corporation 01 Delaware Application July 6,1942, Serial No. 449,972 6 Claims. (or. 266-666) This invention relates to a process for the production of pure or substantially pure cyclohexane from straight run naphthenic petroleum fractions.

The object of the invention is to provide a .process whereby cyclohexane may be more economically produced as a relatively pure chemical from naphthenic petroleum fractions.

cyclohexane, as is known, is a valuable chemical being used as a starting material for the synr .theses of various important products and chemi-' cal intermediates. For such uses a pure or rela-' tively pure cyclohexane is required. At present the available cyclohexane is produced from pure or relatively pure coal-tar benzene by hydrogenation. As a consequence, it i a relatively expensive chemical, of limited ultimate-potential production.

It is known that certain straight run petroleum fractions contain appreciabl quantities of cyclohexane. Attempts to recover this cyclohexane in a pure or relatively pure form have, however, not met with success due to the fact that the yields are quite low and the recovery of pure cyclohexane from the complicated mixture of hydrocarbons in such distillates is far too involved and costly to be practical. Consequently, no attempt is made at present to recover this cyclohexane as such.

. Recently a method has been developed whereby relatively pure cyclohexane may be produced from such distillates. This method, which is described and claimed in copending application Serial No. 334,586, filed May 11, 1940, which issued October 20, 1942, as Patent Number 2,299,716, not only recovers cyclohexane naturally existing in such distillates but produces considerable amounts of additional cyclohexane from the methyl cyclopentane which is invariably found associated with the cyclohexane. According to the method of said copending application, the naphthenic distillate is fractionated to remove all material boiling above cyclohexane and, if desired, a portion of the cyclohexane. The lower boiling material is then subjected to a catalytic isomerization treatment whereby methyl cyclopentane is converted to cyclohexane and certain paraffinic hydrocarbons which are normally present and boil at substantially the same temperature as the cyclohexane are isomerized to lower boiling isomers. As a consequence of this isomerization treatment, the concentration of contaminating hydrocarbons is materially reduced, the concentration of cyclohexane in the fraction is materially increased, and impurities boiling with cyclohexane are altered in boiling point. It is therefore possible by careful fractionation to recover a cyclohexane of nfuch better purity from this isomerized distillate than would be possible from the original distillate. While this method allows the recovery of relatively pure cyclohexane ingood yields from naphthenicdistillates, it does not yield cyclohexane of sufficient purity for 'many of the desired uses. This is due to the fact that the isomerization reactions come to an e'quilibrium before all of the materials are reacted,

and this makes the separation resulting from change of boiling point incomplete. Consequently, in order to produce pure cyclohexanes by this method a further treatment of a, different nature is required.

It has now. been found that equivalent yields of cyclohexane of much better purity may be economically recovered from such distillates by a process which is totally different from the process just described. According to the process of the present invention, cyclohexane of any desired purity is recovered in excellent yields from naphthenic distillates by a combination of steps comprising a simultaneous isomerization and dehydrogenation followed by hydrogenation with suitable intermediate separation of certain materials which ordinarily make the separation of cyclohexane difficult or impossible.

The process of the present invention has been specifically developed for the production and recovery of cyclohexane in a pure or relatively pure form from straight run distillates from naphthenic petroleum, and'more particularly the socalled Cc fractions from such distillates. As will be pointed out below, however, it can also be advantageously applied for the production of certain cyclohexane homologues. Such Ce fractions from such distillates invariably consist of a complicated mixture of hydrocarbons of naphthenic and paraflinic character, often containing small to appreciable amounts of aromatic and/or ole- ,finic hydrocarbons. The paraffinic hydrocarbons are usually of both straight andbranched chain structure, although the normal paraflins usually predominate. The naphthenic hydrocarbons in such fractions consist, in general, of substantial amounts of cyclohexane and methyl cyclopentane, often with minor amounts of other naphthenic hydrocarbons whose boiling points are within or over the boiling range of the distillate. These naphthenic hydrocarbons are often present due to their forming azeotropic mixtures with small amounts of benzene sometimes present.

. treatment or these straight run fractions. it is pparent that it can also be used with distillates of the described compositions regardless of the source. .lhetreatmentofthesedi'stiliatesaccordingto the processof the inventionwillbe describedin connection'with the attached drawing forming a .part of the specification wherein there is shown tion'ated to remove undesired higher boiling materials. Thus, referring to the drawing, the naphthenic straight run gasoline entering via line I v is fractionated in fractionating column 2 and a lower boiling fraction to be n rther treated is taken oil! overhead via line 8. The bottom prodnot from fractionating column l is returned to the refinery. The upper boiling point of the overhead product irom fractionating j column 2 is chosen between about 75 C. d 858C. The exact out point between these-approximate limits determines yield of cyclohexane obtainable and also to a certain extent'determines the emciency ofthe later-described separation, steps and/or the purity of the product ob- -;tained. If the maximum boiling point of the fraction is, for example, 85 C. a maximum yield of cyclohexane will be obtained. If the maximum boiling point of the fraction is, however, 81 CJa purer produ maybe more easily obtained with only a slig tly decreased yield If, onthe other hand, the maximum boiling point of the fraction is, for example, 76, C., the recovery steps are greatly simplified and-a product of 'ex' ceptio'nal purity is easily obtained but the yields are considerably less than maximum.

The overheadproduct from i'ractionating col- "umii I is then preferably subiectedto a second asraers the beneficial 'resultsof the treatmentare onlyobtained with "specific-catalytic agents. Other catalytic agents of the same general type such as the oxides of Cr, T], V, Fe, Ni, 00, Cu, W, etc., do

not give the desired results. While the process iaspecii'ic to use ofmolybdenum oxide, this catalyst may be applied in any of the conventional forms. Thus, it may be used persefas a mixed gel or supported upon a suitable carrier. A preferred catalyst comprises a minor amount of "molybdenum oxide supported upon an active fractionation .to separate lower boiling diluents. a

' This fractionation, although not essential, contributes towards the economy of the process by reducing the-amount of material treated in the subsequent steps in order to produce a given yield of cyclohexane. Thus, the overhead product from fractionating'ooh'unn 2 passes via line 3 to a sec- 0nd fractionating column [wherein lower boiling materials are separated and removed overhead via line I. The maximum boiling point of the overhead product from fractionatingcolumn 4 may be any desired temperature below about 70 C. r The bottom product from fractionating column 4 is a narrow boiling fraction boiling between about not above 70 C. to 75 C.-85 C. and

contains substantially all of the methyl cyclo-. pentane originally present in the n'aphthenic dis- The straight run gasoline fraction leaving fractionator column I via, line 6 is subjected to a catalytimtreatment with a molybdenum oxide cat alysts -It is to be specifically pointed out that *alumina. The alumina may be either alumina alpha monohydrate, gamma alumina or an alumina stabilized by reaction with a small amount of an oxide of an alkali metal or alkaline earth metal. The catalyst may also, if desired. contain relatively small amounts of promoters. A preferred concentration of molybdenum oxide in the described preferred catalyst is-between about 4% and 30% by weight.

The treatment with the molybdenum oxide catalyst is .eflected under conditions quite similar to those employed in catalytic hydroformingwith this catalyst. The temperature of the treatment may bevaried between about 425 ,C. and 550 C., and preferably between about 450 C. and 500 C.

The pressure may be from 3 atmospheres up to about 100 atmospheres butfis preferably between periodically removed by burning in the known manner. I

Thus, again referring to the drawing, the material' to be treated is vaporized and preheated to the desired reaction temperature in furnace 1 and then passed through the reactors 8 and 9 containing the molybdenum oxide catalyst. While one reactor, for example reactor 8, is processing, the other reactor is being regenerated in the known manner by regeneration gases enteringvialine M and leaving via line H. The bydrogengas recycled through the reaction zone with the feed is added in a mole ratio of 1:1 or

r ater to. the feed via line [2. The product passes via line I! to a cooler or heat exchanger It, then to a separator l5, uncondensed gases are compressed iii-compressor I 8 into line I! to he used ih'the subsequent catalytic treatment as .described below. The liquid product from separator I5 is next subjected to a treatment to remove a substantial portion of the paraflinic hydrocarbons which make the ultimate separation of relatively purecyclohexane by fractional distillation difficult or impossible. may be eflected in a number of ways. In such cases where the maximum boiling point of the fractions subjected to the dehydrogenation treatment is below about C., a simple fractionation can be advantageously employed. A preferred method is, however, to fractionate the product in the presence of a higher boiling polar solvent such, for example, as phenol, cresol, aniline, resorcinol, diacetin, or their equivalents.- To this end the product from separator 15 is passed via line l8 to a fractionating column IS." The higher boiling polar solvent enters column 19 near the top via line 20 and is withdrawn from the bottom of line 2|. The overhead product from column l9 consists essentially of undesired material and is removed from the system via line 22. The bottom product from column I9 is passed to a secondary column 23 wherein the higher boiling polar solvent is recovered as a bottom product and recycled back to column l9 via line 20. The overhead product from column 23 passes via line 24, accumulator 25, pump 26, line 21 and preheater 28 to a catalytic converter 29. The converter 29 is supplied with a suitable hydrogenation catalyst. Any of the hydrogenation catalysts commonly employed in the hydrogenation of petroleum fractions and products may be used. Suitable catalysts, for example, are cobalt, nickel, nickel oxide, copper-chromium oxide, copper chromite, nickel-tungsten sulfide, molybdenum sulfide, etc. The reaction conditions in catalytic converter 29 are adjusted, according to the catalyst. to eiiect substantial hydrogenation of olearated from the excess hydrogen and any gaseous products. The hydrogen separated in separator 32 passes via line 33 and valve 34 to line l2 and is thus recycled to the first described reaction zone. In order to avoid excessive dilution of the.

recycled hydrogen with gaseous products, a portion of the recycled hydrogen may be periodically or continuously withdrawn from the system via line 3! and a suitable amount of fresh hydrogen added via line 36.

The liquid product in separator 32 contains some or all of the cyclohexane originally in the gasoline feed stock, depending upon the maximum boiling point or the traction treated, plus cyclohexane produced from the methyl cyclopentane in the feed stock. Also, such amounts of benzene present in the original feed stock may have been largely converted to cyclohexane. It is a crude cyclohexane fraction. Since by the described sequence of steps the constituents which make the fractionation of cyclohexane from straight run gasolines difiicult or impossible have been largely eliminated, cyclohexane of substantial purity may easily be recovered from this crude product by suitable known methods. Generally, a relatively eflicient fractional distillation is suflicient to produce cyclohexane meeting with the usual requirements. Thus, the liquid product from separator 32 is passed via line 31 to a tractionating column 38 wherein lower boiling impurities are removed overhead via line 39 and the residue is directed to a Iractionating column ll wherein the cyclohexane of the desired purity is separated and removed via line 4|. Higher boiling impurities are removed from the system iirgmgshe bottom of iractionating column 40 via While in the above we have described the proces! of the invention as applied in the production of cyclohexane, it is also possible to utilize the process for the production of methyl cyclohexane or dimethyl cyclohexane. In these cases the process is effected in the same manner except that a fraction of the naphthenic straight run gasoline consisting essentially of the hydrocarbons containing seven or eight carbon atoms, respectively, is separated and subjected to the described sequence of treating steps. In the case of the production of dimethyl cyclohexane it is difficult to obtain a pure product. This is due to the greater complexity of the material treated and the number of isomers of the product encountered. In the case of the production of methyl cyclohexane, on the other hand, the process is of exceptional advantage and may, in fact, if desired, be somewhat simplified. Thus, in the production of methyLcyclohexane the liquid product from separator l5 may be subjected to a conventional fractional distillation without the use of the higher boiling polar solvent to remove material boiling up to, for example, 105 C. and the bottom product then passed directly to heater 28 and catalytic converter 29. The fraction separated and subjected to the catalytic treatment with the molybdenum oxide catalyst in this case preferably boils from about 86 C.-93 C. to about 100 C.-104 C.

We claim as our invention:

1. A process for the production of cyclohexane from naphthenic petroleum distiliates of the nature of gasoline which comprises separating from a naphthenic petroleum distillate by fractional distillation a fraction having an initial boiling point below about 70 C. and a final boiling point between about 75 C. and 85 C., said fraction containing substantially all of the methyl cyclopentane naturally occurring in said distillate, treating said fraction under hydroforming conditions in the presence of at least one moi proportion of hydrogen with a catalyst, the pre dominant active constituent of which is molybdenum oxide, removing paraflinic hydrocarbons from the thus-treated product, subjecting the remainder to a catalytic hydrogenation treatment 3. Process according to claim 1 wherein the fraction subjected to the treatment with molybdenum oxide catalyst boils up to about 81 C.

4. Process according to claim I wherein the traction subjected to the treatment with molybdenum oxide catalyst boils up to about C.

5. Process according to claim 1 wherein the fraction subjected to the treatment with molybdenum oxide catalyst boils up to about 85 C. and the removal of parafiinic hydrocarbons is by extractive distillation.

6. Process according to claim 1 wherein the traction subjected to the treatment with molybdenum oxide catalyst boils up to about 75 C. and the removal of parafllnic hydrocarbons is by fractional distillation.

DONALD L. FULLER. BERNARD B. GREENSFELDER. 

